The Relationship between the Pedicle Screw Loosening and Bone Mineral Density after Transpedicular Spinal Instrumentation

Joo, Yong Bum; Yang, Jun Young; Lee, June Kyu; Cha, Soo Min; Kim, Kyung Cheon

Abstract

OBJECTIVES
We have analyzed relationship between pedicle screw loosening and bone mineral densitiy (BMD) after spinal arthrodesis with pedicle screw.
MATERIALS AND METHODS
We have chosen 31 cases that had screw loosening radiologically on the follow up X-ray among the patients who underwent spinal arthrodesis with pedicle screws, and compared Saville's index that was measured by lateral view of preoperative X-ray with Dual energy X-ray absortiometry (DEXA) score.
RESULTS
There were 31 cases (5.34%) with screw loosening among 580cases operated with pedicle screws. According to Saville's index of osteoporosis, 4 cases were grade I, 11 cases were grade II, and 16 cases were grade III, showing statistically significant difference (P<0.05). Each average score of the BMD (g/cm2) of anteroposteior aspect of lumbosacral spine that was measured by DEXA in grade I, II, III by Saville's index were 0.881, 0.782, 0.708. The group with higher Saville's index had the lower score of BMD (correlation coefficient -0.65).
CONCLUSIONS
Osteoporosis is the preoperative risk factor that may occur screw loosening. It is necessary to measure objective and accurate score of BMD, provide additional treatment for osteoporosis and supplementary procedure that increases the stability of screws in the patients of grade II and grade III by Saville's index.